The union has shown its strength this week, as a small bargaining unit - one some management officials quietly say is not absolutely essential to port operations - has essentially shut down much of the ports of Los Angeles and Long Beach, the nation's two largest ports by container volume.

The strikers are members of the Office Clerical Unit - several hundred workers who provide back office functions to most, but not all, of the terminal operators at both ports.

Unlike most longshore units, which sign one contract covering members at all employers along the West Coast, the Office Clerical Unit handles contracts on an employer-by-employer basis, though most of them tend to be negotiated at the same time. At many terminals, clerical workers have been working under terms of contracts that expired in June 2010.

On their own, the clerical workers could not halt operations at the ports. But as soon as thousands of members of other longshore units - crane operators, forklift drivers, container loaders and unloaders, among them - refused to cross picket lines, cargo movement at both ports slowed to a crawl.

The impact has been dramatic. Many ships bound for Los Angeles and Long Beach have sailed to other ports, where some cargo is being unloaded and sent to its final destination. But many of the cargo containers stuck at other ports and bound for the Los Angeles area are simply being stored dockside, waiting to eventually return to Southern California, a port source said.

"It's hard to think of any other union which has such a powerful influence over the economy," said Goetz Wolff, lecturer of urban planning at the UCLA Luskin School of Public Affairs. "The success of the longshore union is in part because they are at a clear intersection of the logistics chain. One doesn't have to be a rocket scientist to learn that's why corporations want to destroy the union."

Management sources and union members say workers in the Office Clerical Unit use computer systems to track cargo on ships and ensure it is routed to the correct truck or train when it is set to leave the terminal for a warehouse or retailer.

Trinie Thompson, a logistics coordinator with terminal operator APL Limited, is in charge of making sure containers move seamlessly from ship to rail. A lot of her job involves making sure a container has the proper clearances to move along the supply chain, she said.

"Let's say we have a container on the ship and it's going to Chicago," she said. "Once the vessel comes in, I'm going to look at all the containers going to Chicago and make sure they have all the requirements to move on rail - that they've cleared customs and the railroads have been billed."

Other members of the bargaining unit handle finances and interact with truck drivers and brokers who want to know how they can find their shipments. Some are even office receptionists.

Management sources say some of the work can be done electronically - at many terminals, customers can generally track their shipments by computer - but they acknowledge some customers like to speak with a person.

The clerks are well paid, a fact not disputed by either side. Stephen Berry, a partner at the Paul Hastings law firm and the lead negotiator for the employers, said full-time clerical unit employees earn $40 or $41 an hour, 11 weeks of paid time off each year and generous pensions.

But the argument is not about pay. Union officials say they are worried some tasks have already been quietly shifted to workers in other states and countries who do the same jobs for lower wages. Management officials deny these charges and say the problem with the status quo is so-called featherbedding - the requirement they provide jobs to temporary and full-time workers when there is no work to perform.

The clerical unit is unusual because most of its members are employees at the terminal operators. When office-type openings at these companies occur, managers are generally allowed to interview candidates and to choose their preferred applicant - provided that person has been vetted by the union. Many other dockworkers typically float from terminal to terminal and are not employees of any one company.

Many ports in other cities do not have separate clerical units, said Kristen Monaco a professor of economics at California State University, Long Beach, who studies the shipping industry. The clerical workers elsewhere are often part of a larger union of longshore workers, Monaco said.

That distinction is important, she said, because bigger unions generally focus on more substantive issues in contract negotiations. A larger entity such as the main branch of the ILWU might also be able to negotiate new types of jobs for clerical workers, if those jobs were deemed no longer necessary.

"There would be other employment opportunities for them," Monaco said.

The clerical unit is almost entirely funded by dues and fees from its members, government records show. The unit reported more than $1.3 million in cash receipts in 2011, a little more than $1.1 million of which came from member dues and fees, according to its most recent Department of Labor filing. Its president, John L. Fageaux Jr., earned $194,093 in salary in 2011 and received total compensation of $222,644, documents show.

At the end of 2011, the clerical unit claimed $245,681 in total assets -- almost all of which was in cash, records show.

The Office Clerical Unit has 631 full-time workers and 175 part-time workers, government reports show. According to the report, 73 people are "agency fee payers" -- usually workers who pay money to the organization but are not considered members.

But despite its small numbers, the Office Clerical Unit has the public support of thousands of other dockworkers.

And while many of them may quietly want to go back to work, Wolff, the UCLA lecturer, said the overall union leaders likely will support the strike until it ends, at least in their public comments.

He said ILWU leaders believe they have a duty to raise wages for all workers - not just those on strike or who are honoring the picket line.

"There are two ways of looking at the high wages these workers have," Wolff said. "One is 'how dare these people make so much money?' The other argument is the ILWU's. In the long run, they want to raise the floor so everyone -- whether they are working in fast food, or as a nurse or in a factory -- gets a higher wage as well.

"They don't think of themselves as having an exclusive right to having good working conditions, rights and benefits."